High-power direct diode lasers are gaining popularity in applications such as heat treating and cutting in the automobile and material processing industries. To heat or cut a material, the radiance of the diode laser has to be high enough to process the material effectively. Manufacturers of diode lasers have developed single-stack and multi-stack diode lasers with an attached collimating lens to collimate light emitted from the fast-axis of diode lasers. Fast-axis collimation is possible to within a few milli-radians of divergence of the laser beam when a collimating lens is used. A collimating lens is typically a rod lens or high numerical aperture cylindrical lens, and each diode laser typically has a collimating lens attached to the fast-axis, which is placed about a few tens or hundreds of microns in front of a facet of the diode laser.
To maintain a perfectly parallel beam of light, the collimating lens has to be placed within a few tens or hundreds of microns from the diode laser facet, with some variational dependence on the optical working distance of the collimating lens. This requires alignment of the collimating lens with the diode laser. It is not easy to passively align the collimating lens to perfectly collimate the laser beam, and many hours of alignment and special tools are usually required to assemble a diode laser package that includes one or more diode laser and the respective one or more collimating lens. Alternatively, alignment of the collimating lens can be provided via active alignment, in which alignment is provided on a real-time basis. However, active alignment can be particularly difficult for a high-power diode stack due to the large number of closely packaged diode lasers.
In the case of a multi-stack diode laser, each individual diode laser has to be collimated and the respective collimating lens is attached to the diode laser package structure. In aligning each collimating lens, the diode laser is running at the operating current and the collimating lens is aligned with a tooling setup that allows for movement of the collimating lens in a four- or five-axis controlled mechanical stage. After the alignment, the collimating lens is attached to the frame of the diode laser by, for example, UV-curing epoxy or a soldering process. However, failure of diode laser alignment is not uncommon. Typically, alignment of the diode laser fails due to weak bonding of the epoxy or degradation of the epoxy joint caused by thermal cycles of the diode laser.
There is, therefore, a need for a novel mechanical structure to align the collimating lens to provide optimal collimation and to hold the collimating lens in place to withstand many thermal cycles of the diode laser.